EP1552950B1 - Printhead to drum alignment system - Google Patents

Printhead to drum alignment system Download PDF

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Publication number
EP1552950B1
EP1552950B1 EP05000172A EP05000172A EP1552950B1 EP 1552950 B1 EP1552950 B1 EP 1552950B1 EP 05000172 A EP05000172 A EP 05000172A EP 05000172 A EP05000172 A EP 05000172A EP 1552950 B1 EP1552950 B1 EP 1552950B1
Authority
EP
European Patent Office
Prior art keywords
print head
drum
contacting
axis
receiving member
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP05000172A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP1552950A3 (en
EP1552950A2 (en
Inventor
David P. Platt
Michael E. Jones
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Xerox Corp
Original Assignee
Xerox Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Xerox Corp filed Critical Xerox Corp
Publication of EP1552950A2 publication Critical patent/EP1552950A2/en
Publication of EP1552950A3 publication Critical patent/EP1552950A3/en
Application granted granted Critical
Publication of EP1552950B1 publication Critical patent/EP1552950B1/en
Ceased legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J19/00—Character- or line-spacing mechanisms
    • B41J19/16—Special spacing mechanisms for circular, spiral, or diagonal-printing apparatus
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/21—Ink jet for multi-colour printing
    • B41J2/2132—Print quality control characterised by dot disposition, e.g. for reducing white stripes or banding
    • B41J2/2135—Alignment of dots
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J25/00—Actions or mechanisms not otherwise provided for
    • B41J25/304—Bodily-movable mechanisms for print heads or carriages movable towards or from paper surface
    • B41J25/308—Bodily-movable mechanisms for print heads or carriages movable towards or from paper surface with print gap adjustment mechanisms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J25/00—Actions or mechanisms not otherwise provided for
    • B41J25/304—Bodily-movable mechanisms for print heads or carriages movable towards or from paper surface
    • B41J25/312—Bodily-movable mechanisms for print heads or carriages movable towards or from paper surface with print pressure adjustment mechanisms, e.g. pressure-on-the paper mechanisms

Definitions

  • the present exemplary embodiment relates generally to an apparatus and a method for maintaining alignment of a print head in a printing system and, more specifically, to an alignment system which needs little or no adjustment during regular use.
  • the present exemplary embodiment is also amenable to other like applications.
  • Ink jet printing involves the delivery of droplets of ink from nozzles in a print head to form an image.
  • the image is made up of a grid-like pattem of potential drop locations, commonly referred to as pixels.
  • the resolution of the image is expressed by the number of ink drops or dots per inch (dpi), with common resolutions being 300 and 600 dpi.
  • Ink jet printing systems commonly utilize either direct printing or offset printing architecture.
  • a typical direct printing system ink is ejected from jets in the print head directly onto a final receiving medium, such as a sheet of paper.
  • the print head jets the ink onto an intermediate transfer surface, such as a liquid layer on a drum.
  • the final receiving medium is then brought into contact with the intermediate transfer surface and the ink image is transferred and fused or fixed to the medium.
  • the print head moves relative to the final receiving medium or the intermediate transfer surface in two dimensions as the print head jets or orifices are fired.
  • the print head is translated along an X-axis while the final receiving medium/intermediate transfer surface is moved along a Y-axis. In this manner, the print head "scans" over the print medium and forms a dot-matrix image by selectively depositing ink drops at specific locations on the medium.
  • Printers of the offset type may employ a single print head which delivers ink droplets to a drum.
  • the drum rotates multiple times during the formation of an image.
  • the print head includes a jetstack or plate which defines multiple jets configured in a linear array to print a set of scan lines on the intermediate transfer surface with each drum rotation. With each rotation, X-axis translation of the print head causes the jets to be offset by one or more pixels, enabling the printer to create a solid fill image, continuous line, or the like, depending on the particular combinations of jets fired.
  • a print head positioner includes a stepper motor that is coupled by a substantially friction- and backlash-free taut metal band to a lever arm that imparts precise lateral motion to a positioning shaft that is rigidly attached to the print head assembly.
  • Each step of the stepper motor is translated by the lever arm into one pixel (0.085 millimeter) of lateral movement of the shaft.
  • the exact amount of translation per step of the stepper motor is adjustable by an eccentrically mounted ball that is minutely positionable on the lever arm.
  • the ball couples angular motion of the lever arm to lateral motion of the shaft such that adjusting the ball position on the lever arm provides a variable scale factor adjustment that compensates for tolerance buildups and exact inter-nozzle spacing on the print head.
  • the shaft is biased toward the ball by a spring. The shaft further allows the print head to swing away from a print media support, such as a drum, for maintenance.
  • the exemplary embodiment may take form in various components and arrangements of components, and in various steps and arrangements of steps.
  • the drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the exemplary embodiment.
  • FIGURE 1 is a simplified block diagram of an exemplary offset ink-jet printing apparatus that utilizes the alignment system of the present invention
  • FIGURE 2 is a top plan view of a drum assembly and print head of the printing apparatus of FIGURE1 ;
  • FIGURE 3 is a perspective view, partially cut away of the drum assembly and print head of FIGURE 2 ;
  • FIGURE 4 is an enlarged perspective view of the print head of FIGURE 2 and a print head drive mechanism
  • FIGURE 5 is an enlarged perspective view of the print head of FIGURE 4 ;
  • FIGURE 6 is a greatly enlarged perspective view of a portion of the print head and drum assembly of FIGURE 3 , showing a point of contact between the print head and drum assembly;
  • FIGURE 7 is a schematic view of a linkage between the drum and print head of FIGURE 2 ;
  • FIGURE 8 is a greatly enlarged perspective view of a left hand end of the print head of FIGURE 2 with a biasing assembly;
  • FIGURE 9 is a sectional view of the left hand end of the print head of and part of the biasing assembly of FIGURE 8 ;
  • FIGURE 10 is an enlarged perspective view of the print head drive mechanism of FIGURE 4 ;
  • FIGURE 11 is a side sectional view of the of the print head drive mechanism of FIGURE 10 ;
  • FIGURE 12 is an enlarged side view of the lead screw and nut portion of the drive member of FIGURE 11 ;
  • FIGURE 13 is an enlarged perspective view of the right hand stub shaft of the print head and a guide rib of the print head drive mechanism of FIGURE 10 ;
  • FIGURE 14 is an enlarged perspective view of a cone and nut assembly of FIGURE 11 engaging the guide rib of FIGURE 13 ;
  • FIGURE 15 is an enlarged perspective view of the print head drive mechanism of FIGURE 11 showing movement directions of the cone and nut assembly;
  • FIGURE 16 is a perspective view of the drum, chassis, and right hand print head bearing of the printing apparatus of FIGURE 1 .
  • the exemplary imaging system 10 is a printing apparatus which utilizes a single print head for performing an offset or indirect inkjet deposition method.
  • Examples of this type of offset ink-jet printing apparatus is disclosed in U.S. Patent No. 5,389,958 (the '958 patent) entitled IMAGING PROCESS, and U.S. Patent No. 6,213,580 for an APPARATUS AND METHOD FOR ALIGNING PRINT HEADS (the '580 patent), which are assigned to the assignee of the present application.
  • the '580 and '958 patents are hereby specifically incorporated by reference in pertinent part. It will be appreciated, however, that the present apparatus and method may also be employed with various other ink-jet printing devices which utilize different architectures, including multiple print head printing devices.
  • the printing apparatus 10 receives imaging data from a data source 12.
  • a printer driver 14 within the printer 10 processes the imaging data and controls the operation of a print engine 16.
  • the printer driver 14 feeds formatted imaging data to a print head 18 of the print engine 16 and controls the movement of the print head by sending control data to a motor controller 19 that activates an X-axis drive mechanism 20.
  • the printer driver 14 also controls the rotation of a transfer drum 26 by providing control data to a motor controller 27 that activates a drum motor 28 .
  • the print head 18 of the print engine 16 includes a jetstack 32 in the form of a perforated plate that extends parallel to the transfer drum 26 .
  • the print head 18 is moved parallel to the transfer drum 26 along an X-axis as the drum 26 is rotated and print head jets or nozzles 33 ( FIG. 3 ) in the form of orifices in the jetstack 32 are fired.
  • Rotation of the drum 26 creates motion in a Y-axis direction relative to the print head 18, as indicated by arrow Y ( FIG. 3 ).
  • Liquid or molten ink is ejected from the print head nozzles 33 onto an intermediate transfer surface 34 ( FIG. 2 ), which forms an outer cylindrical surface of the drum 26.
  • FIGURE 3 which shows a perspective view with the drum omitted for clarity
  • the drum 26 is mounted for rotation on a shaft 36 (shown in phantom).
  • the shaft 36 and drum 26 are the moving parts of a drum assembly 38, the stationary parts of which will be described in greater detail below.
  • the shaft 36 and associated drum 26 are rotated in the direction of action arrow E .
  • an ink image is deposited on an intermediate transfer layer (not shown).
  • the intermediate transfer layer can be a liquid layer that is applied to the drum surface 34 with an applicator assembly (not shown), and may include, for example, water, fluorinated oils, surfactants, glycols, mineral oils, silicone oils, functional oils, and combinations thereof.
  • the ink utilized in the printer 10 is initially in solid form and is then changed to a molten state by the application of heat energy.
  • the molten ink is stored in a reservoir 40, mounted to the print head, and is delivered to the jets 33.
  • the intermediate transfer surface 34 is maintained at a preselected temperature by a drum heater (not shown). On the intermediate transfer surface, the ink cools and partially solidifies to a malleable state.
  • one scan line has an approximate width of one pixel (one pixel width).
  • one pixel has a width of approximately 0.085 mm.
  • the width of one 300 dpi scan line equals approximately 0.085 mm.
  • an alignment system 50 maintains alignment of the print head jetstack 32, relative to the transfer surface 34 of the drum 26 , to minimize unwanted relative movement between the jetstack and the drum during printing.
  • the alignment system 50 thus minimizes unwanted movement (as opposed to the desired X-axis translation of the print head and rotation of the drum), which can result in undesired printing artifacts, such as banding and streaking.
  • an object which is free to move in space has six degrees of freedom, illustrated by perpendicular axes X, Y, Z and rotational axes R x , R y , R z .
  • the present alignment system 50 acts to constrain the jetstack 32 against unwanted movement in all six degrees of freedom, thereby facilitating the use of a larger jet array height j (the vertical height between upper and lowermost jets 33 ) than has been possible with prior systems.
  • the alignment system 50 uses a linkage of components, which will be described in greater detail below. The linkage provides three contact points to define a plane and a fourth point to constrain the print head against rotation. In this way, the print head, and hence the jetstack, are accurately positioned without the need for recalibration once the printer leaves the factory.
  • the alignment system 50 allows each of these alignment parameters to be controlled to maintain print quality, without the need for recalibration. It will be appreciated that the terms “left” and “right” refer to the arrangement of the print head 18 and drum 26 illustrated in FIGURES 2 and 3 .
  • FIGURES 4 and 5 which show one embodiment of a print head 18 with the jetstack removed for clarity, the print head 18 is mounted to left and right stub shafts or journal pins 60, 62 by left and right mounting towers 64, 66, respectively, at opposed ends of the print head.
  • the print head drive mechanism 20 translates the right stub shaft 62 along the X-axis and thus the coupled print head 18 moves in a direction parallel to the X-axis. It will be appreciated that the drive mechanism 20 could, alternatively, translate the left stub shaft 60 , if its position were changed.
  • the X-axis is defined as being collinear with an axis through the stub shafts 60, 62 ( FIG. 5 ).
  • An upper end 68 of the print head 18 can be biased about rotational axis R x in a direction towards the drum 26, by a biasing member or members, such as one or more head tilt springs 70.
  • a single head tilt spring 70 is illustrated in FIGURE 2 , between left and right mounting towers 64, 66.
  • the print head 18 makes contact with the drum assembly 38 at first and second contact points 74, 76, adjacent left and right sides of the print head respectively.
  • the contact points 74, 76 are defined by first and second contacting members 78, 80 ( FIG. 4 ), in the form of hard stops, carried by the print head 18 , and corresponding first and second receiving members 82, 84 in the form of buttons, carried by the drum ( FIG. 3 ).
  • buttons 82, 84 are visible. Additionally, or alternatively, the center of gravity of the reservoir 40 and print head 18, being forward (closer to the drum) than the shafts 60, 62, helps to keep the hard stops in contact with the buttons.
  • the print head 18 includes a front reservoir plate 90 , formed from a rigid material, such as aluminum, which is integrally formed with or otherwise rigidly mounted to the left and right mounting towers 64, 66.
  • the front reservoir plate 90 includes generally cylindrical extension members 92, 94, which extend from left and right sides of the reservoir plate 90, respectively, parallel with the X-axis.
  • the extension members are integrally formed with or otherwise rigidly connected with the front reservoir plate 90.
  • Cylindrical blocks 96, 98 formed from stainless steel or other hardened material, are mounted within the extension members 92, 94, respectively.
  • a front face 100, 102 of each of the blocks 96, 98 defines a generally planar contacting surface of the respective hard stop 78, 80.
  • the hard stops 78, 80 are carried by the reservoir plate 90, in an alternative embodiment, the hard stops are carried by the jetstack 32. In yet another embodiment, the positions of the hard tops and buttons are reversed, with the hard stops being carried by the drum assembly and the buttons being carried by the print head.
  • buttons 82, 84 are mounted to a stationary part of the drum assembly, by generally cylindrical labyrinth seals 110, 112.
  • the buttons can be formed from a resilient plastic or other suitable material which undergoes little or no deformation on contact with the hard stops 78, 80 and which provides a low friction contact with the steel material of the hard stops.
  • the buttons 82, 84 may each have a convex, spherical tip, which provides a single point of contact with the respective hard stop 78, 80, while allowing for any misalignment between the button and the hard stop.
  • the hard stops 78, 80 make sliding contact with the buttons 82, 84 , over the length of travel of the print head.
  • the X-directional width of the contacting surfaces 100, 102 of each of the hard stops is greater than a length of travel of the print head during translation.
  • FIGURE 6 which shows the left hand button 82
  • the buttons are mounted within suitably positioned sockets 113 in peripheral portions 110, 112 of left and right stationary frames 114, 116 .
  • These frames 114, 116 also referred to as "labyrinth seals" carry the bearings for the drum shaft 36 (illustrated in phantom in FIGURE 3 ) via a central aperture 118 formed therein.
  • the sockets 113 extend into the frames 114, 116 to which the buttons are rigidly mounted.
  • the frames or "labyrinth seals" as implemented are formed from cast aluminum. Alternate materials are considered.
  • the head tilt spring 70 biases the upper end of the print head 18 such that the hard stops 78, 80 remain in contact with the buttons 82, 84, as shown in FIGURE 6 .
  • the drum assembly 38 is rigidly mounted to a chassis 120 of the printer.
  • the drum labyrinth seals 114, 116 are mounted by bolts, screws, or the like to the chassis 120.
  • the chassis 120 may be formed from metal, hard plastic, or other relatively rigid material.
  • the chassis 120 forms a part of a three part linkage 122 between the drum labyrinth seals 114, 116 (and hence the buttons) and the hard stops, via the print head drive mechanism 20 and right stub shaft 62 , which constrains the movement of the print head.
  • the linkage 122 includes a first linkage portion 122A, which links the buttons 82, 84 to the labyrinth seals 114, 116, a second linkage portion 122B, which comprises the chassis 120 and links the labyrinth seals with the print head drive mechanism 20 , and a third portion 122C, which links the print head drive mechanism 20 with the hard stops 78, 80.
  • a first linkage portion 122A which links the buttons 82, 84 to the labyrinth seals 114, 116
  • a second linkage portion 122B which comprises the chassis 120 and links the labyrinth seals with the print head drive mechanism 20
  • a third portion 122C which links the print head drive mechanism 20 with the hard stops 78, 80.
  • the biasing assembly 130 includes a bias spring 132, which in the illustrated embodiment, is aligned with the X-axis (i.e., coaxial with the stub shafts 60, 62 ), as far as tolerances reasonably permit. This alignment of the bias spring 132 with the X-axis serves to minimize any unwanted rotation of the print head 18 away from the drum 24 about the axes R y and R z .
  • the bias spring 132 serves to provide a constant bias force on the print head drive mechanism 20.
  • the length of the bias spring 132 allows it to have a low spring rate and to provide a nearly constant force across the range of imaging motion, which in one embodiment, is approximately 4 mm.
  • An end 134 of the bias spring 132 closest to the drive mechanism 20 is mounted to the chassis 120 via a flange 136 , thus fixing the position of the right hand end 134 of the biasing assembly 130 , relative to the linkage 122.
  • a left hand end 140 of the bias spring 132 furthest from the drive mechanism 20 , is mounted to a right hand end of a hook-shaped retaining member 144 .
  • the hook-shaped retaining member 144 is configured to pass below a lower end of the left mounting tower 64 and engage a distal end of the left stub shaft 60 , thereby maintaining the axial alignment of the bias spring 132.
  • the distal end of the left stub shaft 60 defines a concave socket 146 with its midpoint aligned with the X-axis.
  • the hook 144 defines an inwardly extending protrusion 148, which is seated in the socket 146, allowing a small amount of relative movement between the hook and the stub shaft toward the z-axis and/or y-axis to compensate for any slight misalignment between the chassis and the stub shaft 60.
  • the hook 144 and protrusion 148 are removable from the socket 146 for repair or replacement of the print head 18 .
  • the tension in the bias spring 132 in the X-axis direction maintains the X-axis alignment of the hook and the stub shaft 60.
  • the left and right stub shafts form ends of a single shaft which connects the left and right towers 64, 66.
  • the bias spring 132 can be wound around a portion of the shaft which extends between the towers to minimize misalignment with the X-axis.
  • a roll block 150 is carried by the left stub shaft 60.
  • the roll block defines a plurality of bearing faces 152, four in the illustrated embodiment, and a generally axial bore 154, which snugly receives the stub shaft 60 therethrough, and within which the stub shaft is free to rotate.
  • One of the bearing faces 152 makes sliding contact with an upper flat surface 156 of a left hand X-axis bearing 158, which is rigidly mounted to the chassis 120.
  • the weight of the print head 18 is sufficient to provide a downward force on the roll block 150 in the Y-axis direction, keeping the roll block 150 in contact with the left bearing 158.
  • the bore 154 may be asymmetrically positioned, relative to the X-axis, thus providing each face with a slightly different distance from the X-axis, which may vary, for example, by a few micrometers (e.g., 50 ⁇ m). This allows slight variations in the alignment to be accommodated.
  • the block 150 can be rotated, after the print head 18 has been installed in the printer, such that the face 152 which provides the best alignment in the Y-axis is in contact with the left bearing 158.
  • the asymmetry of the bore 154 allows the left stub shaft 60 to be raised or lowered by selection of the side 152 of the roll block that is placed against the left bearing 158 .
  • the flat surface 156 of the bearing allows the block to slide relative to the bearing, for right to left image motion, as well as front to back sliding (Z-direction), so that the print head to drum alignment system 50 is not overly constrained.
  • a force spring 162 is positioned on the stub shaft 60, intermediate the roll block 150 and the left hand end of the hook 144.
  • the force spring 162 biases the block 150 against axial movement along the stub shaft 60.
  • the force provided by the force spring 162 is less than that provided by the bias spring 132.
  • the increasing tension in the bias spring 132 maintains X-axis alignment of the stub shaft 60 and the hook 144.
  • the force spring 162 compensates for any tendency of the block to slip along the stub shaft in the right to left direction by providing a force which exceeds the friction force between the upper surface 156 of the left bearing 158 and the bearing face 152 of the block. In this way, contact is maintained between the right end of the roll block and the left mounting tower 64. In doing so, it assures sliding between the roll block 150 and the left bearing 158 , rather than between the roll block and the left stub shaft 60. This helps to maintain constant and predictable forces which assist in minimizing positioning errors.
  • the print head drive mechanism 20 includes a drive motor 170, such as a stepper motor, which is operatively connected with a lead screw 172 .
  • the drive motor 170 is directly coupled with a first end 174 of the lead screw 172, without any intermediate eccentric gears, so that the motor and lead screw are aligned as close to the X-axis as reasonable tolerances permit. In this way, any tendency for the motor to impart non axial motion to the lead screw is minimized. Additionally, the direct coupling reduces the number of parts in the print head drive mechanism 20, and the stacked tolerances which this can entail.
  • the stepper motor 170 has about 200 steps per revolution and is driven to provide 128 microsteps per whole step.
  • the lead screw can have a pitch of about 18.75 turns per inch (TPI). This provides an addressable resolution of about 0.053 ⁇ m.
  • a motor is coupled to a lead screw by gears as is disclosed, for example, in U.S. Patent No. 6,244,686 (the '686 patent), which is hereby specifically incorporated by reference in pertinent part.
  • the lead screw 172 carries drive member 180 , such as a nut and cone assembly, at a distal end 182 thereof.
  • the nut and cone assembly 180 converts the rotational movement of the lead screw 172 into axial movement in the X-direction.
  • the assembly 180 includes an internally threaded nut portion 184, within which the lead screw rotates. Threads 186 of the lead screw engage the internal threads 188 of the nut portion 184.
  • the nut portion 184 is constrained against rotational movement by a guide member or anti rotation device 190, such as a guide rib, as illustrated in FIGURES 13 and 14 .
  • the guide rib 190 extends generally parallel with the X-axis and can be mounted to a portion of the chassis 120 .
  • the nut portion 184 includes a lateral groove or slot 192 ( FIG. 14 ), which receives the rib 190 .
  • the groove 192 maintains contact with one of the upper and lower horizontal surfaces 194, 196 of the rib during translation.
  • the groove 192 is slightly wider, in the Y-direction, than the rib 190, such that there is a small amount of rotational play permitted between the groove and the rib. So that this limited amount of play does not affect the drum to print head alignment, the printing can be carried out only in one axial direction, which may be in the right to left direction. In this way, the groove 192 always engages the same face of the rib 192 during printing.
  • groove and guide rib may be reversed, by placing the groove on the chassis and a rib on the nut and cone assembly.
  • Other means for limiting rotation of the nut and cone assembly 180 are also contemplated.
  • the nut and cone assembly 180 further includes a cone portion 200, which for ease of manufacture, may be formed separately from the nut portion 184 and welded or otherwise fixedly attached thereto at a right hand end of the cone portion by means of pins 202.
  • the cone portion 200 is generally conical in shape with a tip 204 at its distal end, which may be semispherical, as illustrated, although parabolic or elliptically curved tips are also contemplated.
  • the tip 204 makes contact with the right stub shaft 62.
  • the right stub shaft 62 defines a concave socket 206, similar to socket 146 of the left stub shaft 60.
  • the midpoint of the socket 206 is aligned with the X-axis.
  • the socket is sized to receive the tip 204 therein and allow relative pivoting between the stub shaft 62 and the cone portion 200.
  • the lead screw 172 is nominally aligned with the X-axis, slight variations in alignment inevitably occur, either during assembly or in subsequent use of the printer.
  • the flexible coupling created by the contacting of the right stub shaft 62 with the cone portion 200 allows these small variations to be accommodated by allowing the cone and nut assembly to pivot, relative to the right stub shaft.
  • the bias spring 132 provides a biasing force in the general direction of the motor 170, which maintains sufficient contact between the tip 204 and the journal socket 206 to avoid misalignment of the print head during printing.
  • the nut and cone assembly 180 accommodates any residual misalignment of the lead screw 172 with the print head 18 due to tolerances of the components. Additionally, the assembly 180 accommodates run out of the nut cone assembly (variations along the threaded portion of the nut cone assembly which engage different portions of the lead screw during translation) which cause changes in alignment during translation of the print head. To allow the nut and cone assembly 180 to gimbal at both ends, the threads 188 of the nut portion 184 have a slightly wider diameter than the diameter of the lead screw threads 186, as illustrated in FIGURE 12 . This allows the nut and cone assembly to have a small amount of play relative to the lead screw 172.
  • the nut and cone assembly 180 can pivot slightly in Y and/or Z directions, relative to the lead screw, to accommodate slight misalignment of the lead screw.
  • Arrows A, B shown in FIGURE 15 illustrate how the cone tip 204 can move, relative to the lead screw 172. For example, if the lead screw is slightly lower than the X-axis, the tip 204 of the nut and cone assembly will pivot slightly upward, and the nut portion will move accordingly.
  • the nut and cone assembly could alternatively define a concave distal surface, similar to the socket 206 of the right stub shaft, which receives a convex surface on the right stub shaft, similar in shape to the tip 204 of the cone portion 200 , i.e., the positions of the two shapes are reversed.
  • the linkage provided by the nut and cone assembly 180 is important for several reasons. First, it allows the weight of the print head 18 to rotate the link until the right stub shaft 62 is seated in a right hand X-axis bearing 210 ( FIG. 13 ). Without this, the normal force between the nut and cone assembly 180 and the print head, due to the bias spring 132 , and the resulting friction, could prevent seating of the stub shaft in the bearing 210. Second, it accommodates misalignment between the lead screw 172 and the stub shaft socket 206. This avoids undue pressure on the lead screw which may occur from a rigid connection. Third, the linkage accommodates misalignment due to lead screw radial run out.
  • the illustrated lead screw 172 is not rigidly coupled to the right stub shaft 62.
  • the flexible coupling 180 of the present stub shaft 62 to the lead screw accommodates any slight misalignment between the lead screw and the X-axis, as defined by the stub shafts 60. 62.
  • a rigid coupling may alternatively be employed.
  • the force of the bias spring 132 reduces backlash in the print head drive mechanism 20 by compressing gaps between the stub shaft socket 206 and cone tip 204, the nut portion 184 and the lead screw threads 186, as well as augmenting the preload to a thrust bearing (not shown) of the motor 170 .
  • the lead screw 172 Since the lead screw 172 is not coupled to the stub shaft 62 for reverse movement in the X-axis, it acts as a pusher drive only. Specifically, the cone and nut assembly 184 only pushes the print head 18 in the driving direction (right to left in the illustrated embodiment). The bias of the spring 132 is thus the return force for print head movements opposite to the drive direction (left to right).
  • the right stub shaft 62 is constrained against unwanted movement in the X-axis and Y axis. In the X-direction, the print head drive mechanism 20 and the bias spring 132 control the alignment of the print head. In the Y-direction, the weight of the print head 18 holds the right stub shaft 62 in contact with the right bearing 210 , illustrated in FIGURE 4 .
  • the bearing 210 is mounted to a portion of the chassis 120 (and hence connected with the linkage 122 ).
  • the right bearing 210 defines a curved upper surface 212 which is shaped to receive the stub shaft 62 therein. The curvature of the upper surface 212 can be slightly less than that of the stub shaft 62 such that the constraint provided by the bearing 210 is in the Z direction as well as the Y direction.
  • a keeper (not shown), mounted to a bearing housing 216 constrains the stub shaft 62 against gross upward movement, for example, during transportation of the printer, or when the printer is tipped out of its ordinary horizontal alignment.
  • the six degrees of freedom for the print head body are controlled as follows: The first two degrees of freedom are constrained in that two points of contact are defined by the buttons 82, 84 and the hard stops 78, 80 on the left and right sides of the print head, each point provides a single axis of constraint in the Z axis only. The next three degrees of freedom are constrained in that a third point, defined by the position of the right stub shaft 62, is constrained in the Z and Y axis by the right bearing 210 and in the X axis by the X-axis nut/cone and bias spring 132. The final degree of freedom is constrained in that a fourth point is created by the left bearing 60, which is constrained in the Y-axis only, it prevents rotation of the print head about the print head Z-axis.
  • Tight tolerances between the drum 26 and the labyrinth seal buttons 82, 84 are attained by post machining the buttons, relative to the sockets 113.
  • the diameter of the drum transfer surface 34 is also machined with tight tolerances.
  • the tolerance between the drum labyrinth seals 114, 116 and the X-axis bearings 158, 210 of the print head is controlled by side frames 220 of the chassis, only one of which is illustrated in FIGURE 16 .
  • the most difficult tolerance to control can be the parallelism of each of the chassis side frames. This parallelism only affects roll, which is compensated for by selecting an appropriate orientation of the roll adjustment block 150, as described above.
  • the front reservoir plate 90 includes several alignment pins 230 (three in the illustrated embodiment of FIGURE 4 ), which extend forwardly and are received through corresponding holes 232, 234 in the jetstack ( FIG. 3 ). At least one of the holes 232 is oriented with its major dimension in a generally horizontal direction, while at least another of the holes 234 is oriented with its major dimension in a generally vertical direction. In both cases, the minor dimension of the hole is selected such that the respective pin 230 fits snugly in the hole, with a minimum of play.
  • the front reservoir plate 90 further includes a plurality of posts 240 ( FIG. 5 ).
  • the posts each have a distal end surface, machined flat, which engages a rear surface 242 of the jetstack, as illustrated in FIGURE 2 .
  • notches 243 may be formed in the jetstack around the posts 240 such that only selected ones of the posts are used.
  • a retaining plate or drip plate 244 in cooperation with clips 246, holds the jets stack 32 firmly against the posts.
  • the retaining plate 244 includes a plurality of holes 248 for receiving studs 250 therethrough which screw into corresponding bosses 252 in the front reservoir plate 90 ( FIG. 4 ).
  • the posts 240 and bosses 252 serve as spacers between the jetstack 32 and the reservoir plate 90 .
  • the clips 246 clamp an upper end of the jetstack against the reservoir plate 90.
  • an assembly 254 comprising the reservoir plate 90 (including the alignment pins 230, bosses 252, posts 240, extension members, and left and right hard stops), and left and right stub shafts 60, 62 , and left and right mounting towers 64, 66, is integrally formed of one piece, such as by molding, followed by any machining appropriate.
  • the stub shafts 60,62 may be separately formed and then rigidly attached to the towers 64, 66 .
  • the alignment system 50 thus described maintains alignment of the print head 18 with the drum 26 throughout the printer lifetime, even where slight changes due to wear, warping, or thermal expansion/contraction of the chassis occur.
  • the three key alignment tolerance parameters which affect print quality are all taken into consideration by the alignment system 50.
  • Head-to-Drum distance is controlled by the interface between the hard stops 78, 80 and the jetstack 32 and between the drum 26 and the labyrinth seal buttons 82, 84 .
  • the gap across the entire length of the jetstack between the right and left hard stops is thus maintained within tight tolerances, minimizing HTD skew or yaw.
  • the alignment system also provides stability of the tolerance during shipping and handling.
  • Head height is controlled with the X-axis stub shaft interface by maintaining a tight tolerance between the jet array and the print head X-axis and between the drum labyrinth seals 114, 116 and the X-axis bearings 158, 210.
  • the left side X-axis stub shaft 60 is free to move fore and aft. Pitch and Height, or Hilt, are thus minimized.
  • Head Roll is the only alignment parameter that is adjusted. This is accomplished using the roll block 150 with the eccentric bore 154. Typically, once the block adjustment has been made at the factory, no further adjustments of the block are necessary during the lifetime of the printer.
  • the alignment system enables the print head 18 to be accurately aligned with the drum 26 which avoids the need for subsequent print head adjustments, reduces the extent of engine adjustments, and minimizes the risk of print head damage to the drum.
  • the exemplary drive system 20 is formed with fewer components, reducing the effects of stacked tolerances.
  • the exemplary drive system also allows movement of the print head 18 relative to the drive system in order for the print head to maintain alignment with the transfer surface 34.

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  • Engineering & Computer Science (AREA)
  • Quality & Reliability (AREA)
  • Ink Jet (AREA)
  • Common Mechanisms (AREA)
EP05000172A 2004-01-08 2005-01-05 Printhead to drum alignment system Ceased EP1552950B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US753596 2004-01-08
US10/753,596 US7204571B2 (en) 2004-01-08 2004-01-08 Printhead to drum alignment system

Publications (3)

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EP1552950A2 EP1552950A2 (en) 2005-07-13
EP1552950A3 EP1552950A3 (en) 2008-01-09
EP1552950B1 true EP1552950B1 (en) 2011-06-22

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EP05000172A Ceased EP1552950B1 (en) 2004-01-08 2005-01-05 Printhead to drum alignment system

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EP (1) EP1552950B1 (ja)
JP (1) JP4786905B2 (ja)

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Publication number Publication date
JP4786905B2 (ja) 2011-10-05
EP1552950A3 (en) 2008-01-09
US7204571B2 (en) 2007-04-17
EP1552950A2 (en) 2005-07-13
JP2005193685A (ja) 2005-07-21
US20050151765A1 (en) 2005-07-14

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